The goal of this project is to explain the genesis and control of respiratory pattern in terms of established properties of brainstem respiratory neurons. The experimental approach involves multiunit extracellular recording and neuroanatomical labeling. In recording experiments, neurons are classified into groups based on: 1-anatomical location; 2-discharge pattern in relation to efferent phrenic nerve discharge and; 3-characteristics of the short time scale cross-correlation between unit activity and efferent phrenic nerve discharge. Using this classification as a preliminary functional description of each group of neurons, the interactions within and among these groups are investigated by determining: 1-the response of neurons to test inputs that perturb the respiratory cycle and; 2- the characteristics of the cross-correlation between two units, in either the same or different groups, recorded simultaneously. Neuroanatomical labeling is used to identify afferent and efferent projections of physiologically identified clusters of respiratory neurons.